Process of sizing exploded fibers



Patented Aug. 1, 1950 PROCESS OF SIZING EXPLODED FIBERS Robert M. Boehm, Laurel, Miss, assignor to Masonite Corporation, Laurel, Mica, a corporation of Delaware No Drawing. Application December 1, 1944, Serial No. 566,249

.4 Claims. 1

This invention relates to a process in which the conversion of ligno-cellulose fibrous material to fiber is accompanied by the intimate admixture with the fiber oi resinous materials to provide a furnish for making an improved board or molded product. In general the products made irom such furnish have high dielectric strength and improved resistance to absorption of water which is especially beneficial in obtaining minimum dimensional changes, and minimum warping, and are suitable for water-resistant structural uses, such as switchboard panels, and the like.

The invention has as an object the provision of a process whereby the defibration of the fibercontaining or fibrous material and the intimate admixture of the added resinous materials with the fiber are efiected in a single operation and good retention and thorough distribution of such added materials secured.

A further object is to provide a process of incorporating resinous material with ligno-cellulose fiber which will be productive of a composite furnish, or material for making products of various kinds, having improved plasticity and better fiow in molding operations, and which is adapted for the making of products having improved qualities in respect of properties such as hardness, dielectric strength, water resistance, and wet strength. Additional objects of the invention will be apparent from the following description of modes of carrying the process into effect.

In carrying out the invention, the fibrous material, such as wood, woody material of annual growth, and the like, is preferably preliminarily reduced to comparatively small pieces, such as small wood chips for example, and resinous material is roughly mixed therewith prior to the conversion of the fibrous material to fiber state. The resinous material may be roughly mixed with the wood chips or other partially subdivided fibrous material in various ways; for example, it may be added thereto after being first reduced to small pieces or powder form, or it may be melted and poured over the chips. If desired, such rough mixing may be carried out in the gun chamber referred to below or done as the materials are introduced into the gun.

The conversion of rough mixtures of subdivided fibrous material and resinous material secured in these or other ways to the desiredcomposite furnish is preferably accomplished by means of a gun such as described in U. S. Patent #1324321, to Mason. Having these materials in the gun chamber, steam at high pressures such as 275 to 1200 p. s. i. and corresponding temperatures of 215 to 295 C. is supplied to permeate the materials. The time of holding the materials in the gun chamber under such pressure and temperature conditions is dependent upon the degree of hydrolysis desired in the fibrous material and may be from a few seconds to several minutes. If a relatively high degree of hydrolysis of the fiber is desired, steam at a pressure of about 1000 p. s. i. and corresponding temperature is supplied to the materials in the gun with a holding time of about 10 seconds. Like hydrolysis may be effected with steam at 300 p. s. i. and a holding time of about 30 minutes. If relatively little hydrolysis of the fiber is desired, relatively low steam pressures, as about 300 p. s. i, may be used with a short holding time, as for example about 30 seconds. The steam treatment may be in stages if desired, with preferably increase of pressurein the later stage or stages.

After the materials have been subjected to the steam treatment for the required period of time, the gun discharge valve is opened and the contents of the gun are explosively and disruptively discharged from the high pressure region upon opening a relatively constricted outlet to a region of relatively low pressure, as for example atmospheric pressure. The discharged material is preferably led to a cyclone whereby the steam is permitted to escape and the composite furnish consisting of an intimate mixture of fiber and resinous material is collected.

By the above treatment the fibrous materials are reduced to.a relatively finely-divided fiber mass, consisting partly of ultimate fibers and partly of small bundles of such fibers, and with the resinous material completely or partially melted in the gun chamber and distributed throughout such fiber mass with a high degree of uniformity. The temperature reduction incident to discharge into a region of low pressure and correspondingly low temperature causes hardening of the resinous material on the fiber, where it apparently forms substantially a coating for the constituent fibers and fiber bundles. In case of formation of vapors of the resinous material by the application of the high temperature, these vapors will tend to penetrate into the interior of the ultimate fibers, where they may be condensed.

This thoroughly mixed resinous-fiber material with preferably some additional refining, and some washing, if necessary to reduce or remove content of water-soluble material which may be present, is ready for use. Such material may be formed into sheets either in a relatively dry state or formed from a suspension in water on a forming machine, and made into boards and like products.

By making the furnish from which the sheets are formed in this or equivalent way, losses of the relatively-high-melting-polnt resinous material with efliuent water are substantially minimum and the retention of the resinous material by the fiber is greatly improved as compared with practices such as making the addition of such added resinous material to the fiber after the production of the'fiber has been completed. The resinousfiber material may also be used as a molding material when, reduced to the proper fineness, and when used as a molding compound has excellent plasticity for molding operations.

The resinous materials which have been found suitable for use in the present process are partially or wholly water-insoluble, and have a melting point above about 100 C. and preferably below about 295 C. Melting polnts'between 100 and 200 C. are preferred. Resinous materials which have been found suitable foruse include Vinsol, gilsonite, asphalts, tars, bitumens, cellulose acetate resins, cellulose acetate butyrate resins, ethyl cellulose resins, rosin, pitch, vinyl resins, alkyd resins, phenol-aldehyde resins, urea resins, acrylic resins, polystyrene resins, amino resins, amido resins, coumarone-indene resins, and the like natural and synthetic resinous materials. Vinsol is a resinous material comprising a residue low in abietic acid remaining after the separation of refined rosin high in abietic acid from the resinous material obtained by extraction of pine wood with a solvent. Vinsol is substantially soluble in such solvents as acetone, glacial acetic acid, ethyl, butyl alcohol and the like; it is substantially insoluble in such materials as carbon tetrachloride, petroleum hydrocarbons, turpentine, rosin oil, paraffin wax and the like. A typical analysis of Vinsol which is suitable for use in the present invention is as follows: Melting point (drop method) 115 0.;

acid number 100; toluene insoluble 60%; petroleum ether insoluble 98%; saponification number 158. For description of Vinsol see Chemical Abstracts, volume 29, October 10, 1935, page 6665 Thermoplastic resinous materials are preferred although thermosetting resins may be used. If thermosetting resins are used, it is preferred that relatively slow setting resins be used and the steam treatment in the gun be carried only to such a degree that a partial condensation of the resin will occur during this treatment.

The amount of resinous material to be used is dependent to some degree upon the nature of the final product desired; as, for example, where fiat sheets in the form of a building board are desired, additions of about 5% to 40% of resinous material, preferably about to 25%, based on dry weight of fiber, are satisfactory. For molding materials which require considerable plastic flow, the resinous material content may be relatively high, as up to about 100% based on dry weight of fiber. Molded products have been made with additions as low as 15% of the resinous material; however, the range of about 15% to 50% is preferred.

The following examples are given to illustrate the process and the nature of the products obtained.

Example 1.Hardwood chips, about 1 inch in maximum dimension, were charged into the gun referred to above. Vinsol in the amount of about 15% based on the dry weight of the chips was melted and poured on the chips in the gun. The

melting point of the Vinsol used was about 120 c. (The same Vinsol was used in Examples 2,

4 3, and 6.) Petrolatum in the amount of about 234% on dry weight of chips was also added as a sizing material. Steam was admitted to the gun and preheating performed by raising the steam pressure to approximately-600 p. s. i. in about 45 seconds, after which the pressure was immediately increased to about 1000 p. s. i. This high steam' pressure was maintained for about 3 seconds and then the gun contents were converted into fiber intimately commingled with Vinsol by explosive discharge from the gun chamber.

After washing and refining, the furnish so obtained was formed from a water-suspension into sheets/ or laps and dried, and the moisture content adjusted to about 5%. Such sheets were pressed for about 7 minutes at a pressure of about 1000 p. s. i. between platens heated to about 230 C. During the early part of the pressing operation, the press was breathed; thatis, the pressure was released at intervals to permit escape of steam formed from the moisture in the sheet. The sheet products were then removed without chilling the press platens.

Ablank was prepared under the same conditions as those specified above except that no Vinsol was added to the charge in the gun.

Physical properties of the products so obtained were as follows:

In determining "bond strength samples were pulled apart by force applied normally to the surfaces. Percent residual strength is ratio of M. O. R. after 24 hours immersion in water to M. O. R. dry.

Example 2.-Hardwood chips were charged into the gun, and powdered Vinsol in the amount of about 20% based on dry weight of chips was sprinkled into'the body of chips. The material was preheated by bringing the steam pressure up to about 600 p. s. i. in about 30 seconds; then the steam pressure was quickly raised to about 1000 p. s. i., which pressure was held for about 15 seconds; and then the sun contents were discharged.

The Vinsol and fiber mixture so produced was refined, formed into laps, dried, and then heated for 30 minutes at C. A two-ply lamination thereof was pressed for about 15 minutes at a pressure of about 1500 p. s. 1. between platens heated to about C., followed by chilling the platens below 100 C. while maintaining said pressure on the product. In the substantially complete absence of water plasticizer in this case, the Vinsol present served eflectively for plasticizing purposes. 'The product thus made hail the high dielectric strength of 476 volts per m Example 3.-Hardwood chips were charged into the gun, and powdered Vinsol in the amount of 15% based on the dry weight of chips was sprinkled into the mass of chips in the gun. Steam for preheating was admitted to the gun chamber at such a rate that after 30 seconds the steam pressure had been raised to about 600 p. s. i., which pressure was held for about 45seconds, and the gun contents were then discharged. This furnish was refined, and made into paper, containing approximately 85% of the proportion of Vinsol originally added.

Several sheets of this dry paper were formed into a stack which was pressed for about 15 minutes at a pressure of about 2000 p. s. 1. between platens heated to about 185 0., followed by chilling the platens to about 60 C. while maintaining said pressure on the product. Here again the Vinsol was relied upon for plasticizing eifect.

A blank was prepared under the same conditions as those specified above, except that no Vinsol was added to the charge in the gun, and was subjected to the same pressing conditions.

Physical properties of the products so made are given below:

Plasticity Index.

The plasticity index was determined by dividing the original dry weight in pounds per square foot by the average caliper in inches of the piece after it has been molded, fins and other extruded parts being disregarded in calipering. A higher plasticity index figure is indicative of greater plasticity.

Example 4.--Wood chips, in the proportion of about pine chips and V hardwood chips, were charged into the gun, and asphalt of melting point about 175 to about 185 C. in the amount of on dry weight of chips was sprinkled into the chips. Equal proportions of stearic acid and alum in the amount of about 1% based on the weight of the asphalt was added for sizin material. Steam was admitted to the gun and the materials preheated at a steam pressure of 275 p. s. i. for about 30 seconds, and then the steam pressure was quickly raised to 1000 p. s. i. whereupon the gun contents were explosively discharged.

The furnish so produced was screened, refined, and formed into sheets. The sheets containing approximately 55% to 60% of water on weight of sheet were pressed in a heated hydraulic press with a wire screen for moisture escape against one surface of the sheet at an initial pressure of about 400 p. s. i., and the pressure was then reduced to about 180 p. s. i. The temperature of the platens was about 220 C. The total pressing time was about 9 minutes.

A blank was made under the same conditions except that no asphalt was added to the chips in the gun.

The physical properties of the products were as follows:

Example 5.Pine chips were charged into the gun and powdered Vinsol in the amount 01' 15% on weight of dry chips was sprinkled into the mass of chips. Steam was admitted at sucha rate that in 30 seconds the pressure was raised to 600 p. s. 1., after which the pressure was immediately raised to 1000 p. s. i. and this pressure held for about 20 seconds, and then the gun contents were explosively discharged. The furnish so produced was refined and formed into a sheet and dried until substantially all the moisture was removed.

The sheet was placed in a press and molded under pressure of 2500 p. s. i. and at a temperature of about 190 C'. for a period of about 30 minutes. followed by chilling the mold to about 60 C. while maintaining said pressure on the molded piece.

The molded product had the following physical properties:

Caliper in inches .188 Modulus of rupture dry, p. s. i 7100 44 hr. water absorption:

Percent uptake .74 Percent swell .5 Plasticity index 8.72

Example 6.Hardwood chips were charged into the gun, and granular ethyl cellulose resin in the amount of 15% based on the dry weight of chips was addedto the chips in the gun. Steam was admitted to the gun for preheating at such a rate that the pressure was raised to 600 p. s. i. in about 30 seconds, and then the steam pressure was raised to 1000 p. s. i. whereupon the gun contents were explosively discharged.

The furnish so produced was refined, screened and washed. Petrolatum in the amount of 2% based on the dry weight of the chips was added to the washed furnish as a sizing material. The furnish was formed into sheets and dried, and the dried sheets placed into a humidifier until their moisture content was about 5%.

Four sheets of this material were arranged into a stack with a thermosetting adhesive placed between successive sheets of the stack. The stack was pressed at about 1500 p. s. 1. between platens heated up to about C. and then held at this temperature for 5 minutes, followed by chilling the platens to about 50 C. while maintaining said pressure on .the product.

A blank was prepared under the same conditions as those specified above, except that no ethyl cellulose was added to the charge in the gun.

Physical properties of the products so made are given below:

Ethyl Cellulose Blank Product Specific Gravity 1.38 1.38 Modulus of Rupture. p s 12,990 12,587 Bond Strength. p. si. i 745 25 1 Water Absorption:

24 hr.-Per Cent Uptake 9 2. 3 48 hr.Per Cent Uptake 1.3 3.5 24 hr.Per Cent Swell 8 l. 0 48 hr.Per Cent Swell 1. 1 2. 7 Alkali Resistance:

24 hr.-Per Cent Uptake 8.6 33. 'l 48 hr.-Per Cent Uptake 12. l 43. B 24 hr.-Per Cent Swell 11.3 36. 0 48 hr.-Per Cent Swell 15. 1 i7. 0

In the foregoing examples various temperatures and pressures have been referred to in connection with treatment of the materials in the gun and pressing of the products in the press.

These temperatures and pressures may be varied widely, that is, above and below those specified in the examples, depending upon the characteristics desired in the products.

It will be seen that the addition of the resinous material to the chips prior to their defibration into fiber has many advantages. In the products made from furnishes obtained by the procedure, as described, either in the form of sheet material or molded articles, the bonding properties of the lignin in the wood or other lignocellulose material are supplemented by the additional bonding properties of the resinous material which is intimately distributed throughout the fiber and as so distributed is caused to fuse or substantially fiow during the hot-pressing of the products. The products made from such furnishes have improved properties including better resistance to absorption of water, improved alhall resistance, greater residual strength, and increased dielectric strength as compared with blanks. The procedure is relatively inexpensive because reduction of fibrous material to fiber and intimate incorporation of thermoplastic resinous material therewith are accomplished in a single step, and considerable savings are effected in raw material used.

It is to be understood that the invention is not limited to specific details of the procedural steps and the examples described and which may be varied, but is of the scope defined by the claims.

I claim:

1. Process of making an intimate admixture of resinous material and iigno-cellulose fiber which comprises placing roughly divided fibrous ligno-cellulose material and resinous material having a melting point between 100 C. and 200 C. into a closed chamber, subjecting these materials in the chamber to high steam pressure within the range of 2'75 to 1200 pounds per square inch and corresponding high temperature for a period of time sufficient to cause the resinous material to fuse, and explosively discharging the material into a region of reduced pressure and having a temperature below the melting point of the resinous material, whereby the fibrousmaterial is defibrated into fiber form and the resinous material is substantially uniformly distributed throughout the fiber and is hardened on the fiber by the temperature reduction following discharge, said resinous material being present in quantities between 15 and 25% based on the dry weight oithe fiber.

2. The process as defined in claim 1, and wherein the resinous material is an asphaltic material.

3. The process as defined in claim 1, and wherein the resinous material is a synthetic resin.

4. The process as defined in claim 1, and wherein the resinous material comprises a residue low in abietic acid remaining after the separation of refined rosin high in abietic acid from the resinous material obtained by extraction of pine wood with a solvent.

ROBERT M. BOEHM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,047,170 Asplund July 14, 1936 2,264,189 Richter Nov. 25, 1941 2,317,394 Mason Apr. 27, 1943 2,325,055 Heritage July 27, 1943 2,392,163 Lewis Jan. 1, 1946 2,402,160 Heritage June 18, 1946 FOREIGN PATENTS Number Country Date 635,205 Germany Sept. 12, 1936 OTHER REFERENCES Manufacture of Pulp and Paper, published by McGraw-Hill Book Co., New York, 3d edition, vol. 5, sec. 1, p. 292 (1939).

Mechanical Engineering, July 1943, pp. 515 to 517. 

1. PROCESS OF MAKING AN INTIMATE ADMIXTURE OF RESINOUS MATERIAL AND LINGO-CELLULOSE FIBER WHICH COMPRISES PLACING ROUGHLY DIVIDED FIBROUS LIGNO-CELLULOSE MATERIAL AND RESINOUS MATERIAL HAVING A MELTING POINT BETWEEN 100*C. AND 200* C. INTO A CLOSED CHAMBER, SUBJECT THESE MATERIALS IN THE CHAMBER TO HIGH STEAM PRESSURE WITHIN THE RANGE OF 275 TO 1200 POUNDS PER SQUARE INCH AND CORRESPONDING HIGH TEMPERATURE FOR A PERIOD OF TIME SUFFICIENT TO CAUSE THE RESINOUS MATERIAL TO FUSE, AND EXPLOSIVELY DISCHARGING THE MATERIAL INTO A REGION OF REDUCED PRESSURE AND HAVING A TEMPERATURE BELOW THE MELTING POINT OF THE RESINOUS MATERIAL, WHEREBY THE FIBROUS MATERIAL IS DEFIBRATED INTO FIBER FORM AND THE RESINOUS MATERIAL IS SUBSTANTIALLY UNIFORMLY DISTRIBUTED THROUGHOUT THE FIBER AND IS HARDENED ON THE FIBER BY THE TEMPERATURE REDUCTION FOLLOWING DISCHARGE, SAID RESINOUS MATERIAL BE ING PRESENT IN QUANTITIES BETWEEN 15 & 25% BASED ON THE DRY WEIGHT OF THE FIBER. 